Yup under the axle tube or differential.
If truck is empty I’ll jack it up under a shock mount or a control arm mount, but not with a load.
6000 lbs is a pretty cheesy Jack for the back of a fully loaded truck/camper. Although your camper is lighter than some, I’d ditch the contraption for a simple 10 ton bottle jack and a few squares of 3/4” or thicker plywood which double as camper jack pads and leveling pads to level up the truck when camping.
2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
2017 Heartland Torque T29 - Sold.
Couple of Arctic Fox TCs - Sold